Hi and welcome. Where are you in the uk ? If you are in London i can let you know the details of the colleges that offer the MTI diploma,they are also some outside fo london so let me know where you are.
Like Paul said there are many courses to choose from and at various prices and lengths.
Personally i think anything shorter than a 'school'year is a bit too much to cram in, go for a course that feels right in terms of the massage they teach, you may want a more beauty oreintated course, or more clinical,or general.
Have a look at what available at your local adult ed colleges and go from there as those tend to be better value for money.You needd to do a course that contains he anatomy and physiology also and that the diploma is a recognised one that means you can get insurance to practice.
paul